PubMed Health⌕ Search

Biomedical subjects

F H Johnson

Publications and source records attributed to F H Johnson.

At least 37 records · Page 2Linked to original sources
PubMed1972

Reactions involved in bioluminescence systems of limpet (Latia neritoides) and luminous bacteria.

Luminescence in Latia involves a specific flavoprotein enzyme ("luciferase"), which has a tightly bound flavin group constituting the light-emitter. The overall reaction includes oxidation of a specific substrate ("luciferin," an enol formate derivative of an aliphatic aldehyde), by 2 O(2) molecules, in the presence of a "purple protein" cofactor, yielding a ketone, HCOOH, CO(2), and light. In Achromobacter, a required aliphatic aldehyde, which is functionally equivalent to Latia luciferin, is oxidized to an acid containing the same hydrocarbon chain as the aldehyde; this reaction proceeds in the presence of bacterial luciferase and reduced flavin mononucleotide with a quantum yield of 0.17 + 0.1 photons per aldehyde molecule that is independent of aldehyde chain length from 9 to at least 14 carbons.

Alcaligenes↗
PubMed1971

The elastomeric rack in biology.

A model designated "The elastomeric rack" is discussed with reference to the mechanism of enzyme catalysis and the necessity of large protein molecules in the process. This model, which represents an extension of the earlier "Rack mechanism," stems from experimental evidence demonstrating large volume changes of activation or of reaction accompanying various biochemical reactions and more complicated physiological processes. For reasons discussed, the volume changes, as revealed through the influence of increased hydrostatic pressure on reaction rates and equilibria, prove that there are large conformational changes in the protein which, because of numerous cross links in a complex network, lead to additive stress on the substrate-enzyme complex, and thereby to increased reactivity. The manner in which the model serves to account for the influence of changes in the environment (temperature, pressure, chemical composition, electrical fields) on the activity of the protein catalyst, and the modifying action of particular inhibitory or activating substances, alone or in combination, is briefly discussed. The bearing of various considerations on protein denaturation, excitation of nerve, contraction of muscle, specific precipitation, and the divers physiological processes in living cells, including mutation, cancer, and the degenerative diseases of aging, is also briefly discussed.

Catalysis↗
PubMed1968

Chaetopterus photoprotein: crystallization and cofactor requirements for bioluminescence.

The Chaetopterus photoprotein has been isolated in an amorphous form (molecular weight, 120,000) whlich in (NH(4))(2)SO(4) sollutionl converts to a crystalline form (molecular weight, 184,000) having the same specific light-emittinig activity; quantum yields are 0.0093 and 0.0143, respectively. Two new cofactor reqluirements have been separated fronm impure extracts: a macromnolecule resembling a nucleoprotein, and a lipid-like substance.

Animals↗